如何使用Spark Sql连接null列？

import org.apache.spark.sql.functions._

val df = spark.read.format("csv").option("header", "true").load("data.csv")
val filteredDF = df.filter(col("columnName").isNull)

import org.apache.spark.sql.functions._

val df = spark.read.format("csv").option("header", "true").load("data.csv")
val replacedDF = df.withColumn("columnName", coalesce(col("columnName"), lit("replacementValue")))

val df1 = spark.read.format("csv").option("header", "true").load("data1.csv")
val df2 = spark.read.format("csv").option("header", "true").load("data2.csv")

val joinedDF = df1.join(df2, Seq("columnName"), "inner")